Generally, digital conference arrangements combine information samples representing, for example, speech from various conferees and then distribute the resulting sample to each conference port. One such arrangement is described in the application of M. A. Marouf and P. W. Vancil, entitled "Method and Apparatus for Controlling Ports in a Digital Conference Arrangement", Ser. No. 382,672, filed May 28, 1982. In the Marouf-Vancil arrangement, only samples from selected ports are included in the resulting output sample to reduce noise, echo, and other types of distortion. This is accomplished by assigning each port a priority level based on the state of the port in each one of two sets of states and including in the output sample the information sample of only those ports having predetermined priority levels. By way of example, one set of states may comprise the levels of speech represented by the information samples on the port, whereas the other set may comprise a conferee's history of activity on the port, such as how long the conferee has been silent, how long the conferee has talked, the interval between speech bursts, etc.
In addition, it is desirable to designate a port as having, for example, attendant or originator priority to preempt other speakers. This permits an attendant or conference originator to be always heard by the other conferees. However, the problem with the prior art is that information samples from a designated port are always included in the output sample throughout the entire period of the conference, thereby introducing noise and other types of distortion into the conference even when the conferee on the port is silent.